Photo-catalysis is a process of advanced oxidation that has been successfully used in decontaminating air and water. For decontamination of hydric resources, photo-catalytic reactors have been used at laboratory scale, but it is up to Engineering of chemical reactions to find the most suitable reactor for a given application at commercial volumes.
Prior studies have been conducted to evaluate the performance of different reactors at laboratory scale, which use artificial radiation provided by UV lamps (Dijsktra et al., 2001). However, the information is more limited regarding comparative studies of several types of reactors at pilot scale and which use solar radiation (Blanco et al., 2001).
This work is part of a more detailed study on the performance of several photo-catalytic equipments based on TiO2 as catalyst. The objective of this invention is to provide a process for the design and construction of a reactor at pilot scale or industrial employing information furnished in previous works, considering all the practical aspects decidedly influencing the efficiency of the photo-catalytic process for treatment of residual waters with recalcitrant compounds.
One of the indispensable factors for developing the photo-catalytic reaction is the photonic component, without which said reaction would not be possible. In this sense, the optical properties of the photo-reactor (collectors and absorbers) and the catalyst are of utmost importance when designing these types of reactors. Another aspect to consider is the reactor's hydrodynamic performance because it must guarantee an adequate mass transfer between the contaminant substrate and the catalyst for the photo-catalysis process to be efficient.
The compound parabolic collectors (CPC) are non-concentrator high-efficiency radiation technologies for photo-chemical applications (Malato, 2004a). The present invention provides the process conditions of a pilot plant that will use a CPC as photo-catalytic reactor to eliminate recalcitrant contaminants from residual waters from a variety of industries like the printing industries that use printing inks, and the diverse agricultural industries that use pesticides.
The international document, WO2005/121030, introduces an integrated device for water decontamination and electric energy production. It consists of a hybrid photo-catalytic-photo-voltaic system comprising a photo-catalytic reactor fabricated with material transparent to visible solar radiation and using titanium dioxide, iron (II) or iron (III) as catalyst, which is superimposed to a photo-voltaic panel, both on the same support susceptible to inclination with an adequate angle to optimally avail of the incident radiation. The photo-catalytic reactor protects the photo-voltaic panel from solar ultraviolet and infrared radiation, absorbed by the photo-catalyst and the water, respectively. A recirculation pump, whose electric input is provided by the photo-voltaic panel, ensures the flow of water through the photo-catalytic reactor, which additionally cools the photo-voltaic panel. This invention is of special use for water purification in remote sites.
Request WO2004/089525 presents catalysts for photo-chemical processes with characteristics far superior in photo-catalytic performance when compared to pure titanium dioxide. The compounds are a combination of titanium dioxide with a photo-sensitive coloration capable of mediating in the photo-catalytic process by using the incident radiation in wave lengths that do not promote excitation of the pure catalyst. The photo-sensitive coloration, once excited, promotes electron transfer to the catalyst conduction band enhancing the photo-catalytic action. Treatment of waste water by using these types of compounds is capable of employing photons in a broad range of the electromagnetic spectrum.
The French request, FR2856052, shows a water-treatment plant comprising a conical tower, through its transversal section it has a duct through which a current of contaminated water is fed, then that current is deposited by gravity towards an external spiral channel in which the water current is subjected to 12 different treatments to retain materials suspended in it. The treatments are: adsorption, absorption, aerobic and anaerobic biodegradation, extraction, oxidation, and oxidation by solar photolysis and photo-catalysis or with artificial UV radiation provided by electric lamps and laser beams, and metabolite separation.
European document EP 0334078 introduces an application of the heterogeneous photo-catalysis process to clean a water current by removing an herbicide known as bentazone. Aqueous bentazone solutions at a concentration of 50 ppm are exposed to an ultraviolet radiation wave length above 340 nm. This radiation is generated from a light source with a spectral distribution simulating solar radiation; titanium dioxide is used as catalyst.
Request WO 03014030 introduces an apparatus for water disinfection and a method to inactivate or destroy microorganisms and organic matter present in water. The treatment method consists of adding hydrogen peroxide to contaminated water, introducing the water with peroxide into the photo-catalytic reactor, which has a porous bed, then air is injected into the reactor and UV radiation is provided inside it.
Document WO 02083570 presents a method and an apparatus for photo-voltaic purification of water. Water with organic and inorganic contaminants is fed onto a permeable, open-cell semiconducting unit. Within the unit, a semiconducting surface is capable of acting as a promoter of electronically active sites when exposed to a light source. The catalyst used is titanium dioxide.
The United States request, US2003211022, indicates a device to treat and decontaminate water containing organic agents or biological agents like viruses and bacteria. The device uses an inert substrate to support a photo-active catalyst, which can be titanium dioxide; some high-energy radiation (especially UV) transmission media are also included. The matrix presents a large surface, which is in direct contact with the contaminated water. Radiation that can be provided by a UV lamp is transmitted through the substrate. The substrate introduces media to interact with the photo-active catalyst and organic matter in the water. The photo-active catalyst accelerates decomposition of organic matter present in the water.
Document US2007020158 reveals a system and procedure to treat contaminated water through a photo-catalytic process. The system is comprised of a reservoir in which organic and inorganic contaminants present in water are decomposed. The system includes a recirculation subsystem with a main unit, input pipes connected to the main unit, output pipes connected to the main unit, a pump to recirculate the water, a filter inside the main unit, photo-catalytic processing media placed after the filter and which include a catalyst transporter, and a UV lamp. There is also an electrode unit inside the contaminated water reservoir, with which the water is electrolyzed.
Although patent literature reveals that different devices or reactors have been used to carry out said treatment by employing artificial UV sources (electric lamps) or through solar radiation and that as a general rule, titanium dioxide in anatase crystalline structure is as catalyst; however, there is need to improve processes and equipment for treatment of water contaminated with recalcitrant substances.